what do you mean by "account"?
you should not use bitcoin-cores account feature for a site as the result wont be what you think (please search in the tech section for the exact reason).
I mean every time when user wins the wallet transfers money from main account to user's account. User is able to manage the coins related to his account.
Here is an example.
{
"account" : "",
"category" : "move",
"time" : 1452705552,
"amount" : 12345.00000000,
"otheraccount" : "user890",
"comment" : ""
}